Development of 1GHz Clocked Entangled LEDs for Fibre Networks
Semiconductor quantum dots (QD)s have been well established as sources of single photons and entangled photon-pairs, both of which are essential for realising quantum networks. To be compatible with real-world applications, such a source must further conform to basic requirements including operation at telecom wavelengths and high clock rates. Today, most quantum dot experiments are carried out with sophisticated and bulky research-grade equipment, restricting their use to within laboratories. In this work, a high clock rate entangled photon-pair source for deployment in an existing fibre network is developed. Alternatives to components within the experimental system which are incompatible with deployment are also investigated. To remove the requirement for laser excitation, the quantum dot entangled LED (ELED) is electrically pulsed. The ELED, which is fabricated using standard semiconductor processing techniques, is designed for high clock rate operation at 1GHz, with an in-laboratory entanglement fidelity of 89%. As the entangled photons emitted by the ELED are at telecom wavelengths, 1GHz clocked entanglement distribution over an installed fibre network in Cambridge is demonstrated between two points 4.6km apart. Over the course of a 14 hour experiment, an average entanglement fidelity of 79% is achieved showing excellent stability of the system. In order for entangled photon-pair experiments to be performed outside of a laboratory environment, both the source and detection systems are re-examined. In the detection system, the research-grade single-photon detectors are replaced by self-differencing avalanche photodiodes which have been used in quantum key distribution systems, with an entanglement fidelity of 71% achieved. In the source system, the free space spectral filter which required precise alignment is replaced by a fibre-based spectral filter. As the cryostat in which the ELED was previously cooled required a supply of liquid helium, thus confining the ELED to a laboratory, the operation of the ELED inside a compact closed-cycle cryocooler module is demonstrated.
Quantum communication, Quantum dot, Semiconductor physics, Entanglement
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